(0.4-x)x2=0.4x(1+50%)
0.8-2x=0.4x1.5
0.8-2x=0.6
0.8=0.6+2x
0.6+2x=0.8
2x=0.8-0.6
2x=0.2
x=0.2÷2
x=0.1